One of the major emphases of this proposed work is to understand the importance of the tissue interactions that occur during early embryonic notochord and adjacent somites. In vivo and in vitro studies have shown that the embryonic notochords stimulate somitic mesenchyme to undergo chondrogenesis. The notochord synthesized both proteoglycans and collagen Type 11, the molecules characteristic of cartilage matrix. We have shown that exogenous matrix components are capable of stimulating somite chondrogenesis. Of various artificial matrices used, that composed of proteoglycan/collagen Type 11 appears to be the most effective. We will continue these studies to better characterize the transition in proteoglycan synthesis that occur during development. We will also characterize and determine transitions in collagen types during chondrogenesis.